A Study of the Safety and Efficacy of TRTL-913 in Healthy Volunteers (Part A) and in Adults With Tinnitus (Part B)

Part A Inclusion Criteria:

1. Healthy male or female adults aged 18 to 64 years (or 65 to 80 years for an elderly cohort, if enrolled), as determined by the investigator.
2. Able and willing to provide written informed consent and comply with all study procedures.
3. Body mass index (BMI) 18.0 to 35.0 kilograms per square meter (kg/m\^2) and body weight greater than (>) 50 kilogram (kg).
4. Clinically acceptable medical history, physical examination, vital signs, clinical laboratory tests, and 12-lead ECG, as determined by the investigator.
5. QT interval corrected using the Fridericia method (QTcF) of less than or equal to (≤) 450 millisecond (msec) for males or ≤470 msec for females.
6. Nonsmokers or light smokers (\<10 cigarettes/week or equivalent vaping) for at least 3 months before dosing and willing to abstain during confinement.
7. Women of childbearing potential must have a negative pregnancy test and agree to use highly effective contraception throughout the required study period.
8. Male participants must agree to use appropriate contraception and refrain from sperm donation for the required study period.

Part B Inclusion Criteria:

1. Male or female adults aged 18 to 64 years.
2. Able and willing to provide written informed consent and comply with study procedures.
3. Diagnosis of subjective, stable, chronic, non-pulsatile tinnitus.
4. Generally healthy aside from tinnitus, with no clinically significant abnormalities on medical history, physical or neurologic examination, vital signs, laboratory tests, or ECG that would interfere with study participation.
5. BMI 18.0 to 35.0 kg/m\^2 and body weight >50 kg.
6. Willing to discontinue prohibited medications and substances before study treatment and throughout study participation.
7. Women of childbearing potential must have a negative pregnancy test and agree to use highly effective contraception throughout the required study period.
8. Male participants must agree to use appropriate contraception and refrain from sperm donation for the required study period.

Exclusion Criteria:

Part A Exclusion Criteria:

1. Any clinically significant acute or chronic medical condition that, in the investigator's opinion, could affect participant safety or study assessments.
2. Use of prohibited medications, including moderate or strong cytochrome (CY)P450 inhibitors or inducers, or other prohibited foods or supplements before dosing.
3. History of seizures, epilepsy, significant head injury associated with loss of consciousness, or other conditions or medications that increase seizure risk.
4. Clinically significant cardiovascular disease, clinically significant ECG abnormalities, long QT syndrome, torsade de pointes, or a family history of long QT syndrome or sudden cardiac death.
5. Active infection or clinically significant recent illness before screening or dosing.
6. Positive test for human immunodeficiency virus (HIV), hepatitis B, or hepatitis C.
7. Clinically significant hepatic or renal impairment or clinically significant laboratory abnormalities.
8. History of malignancy within the past 10 years (except adequately treated nonmelanoma skin cancer or cervical carcinoma in situ).
9. Current or recent substance or alcohol use disorder or positive drug or alcohol screening.
10. Current or history of clinically significant psychiatric illness or suicidal ideation or behavior that would increase study risk.
11. Pregnant, breastfeeding, or planning pregnancy during the study.

Part B Exclusion Criteria:

1. Current use of, or plans to initiate, pharmacologic or non-pharmacologic treatment for tinnitus during the study.
2. Regular night-shift work that could interfere with study assessments.
3. Use of prohibited medications, including moderate or strong CYP450 inhibitors or inducers, or other prohibited foods or supplements before dosing.
4. History of seizures, epilepsy, significant head injury associated with loss of consciousness, or other conditions or medications that increase seizure risk.
5. Clinically significant acute or chronic medical condition that, in the investigator's opinion, could affect participant safety or study assessments.
6. Positive test for HIV, hepatitis B, or hepatitis C.
7. History of malignancy within the past 10 years (except adequately treated nonmelanoma skin cancer or cervical carcinoma in situ).
8. Current or recent substance or alcohol use disorder or positive drug or alcohol screening.
9. Current or history of clinically significant psychiatric illness or suicidal ideation or behavior that would increase study risk.
10. Pregnant, breastfeeding, or planning pregnancy during the study.